1904.J Catalysis ~by Colloidal Metals and similar Substances. 367 



the magnitude of a constant from the formula we have deduced on 

 Nernst's hypothesis might, perhaps, seem an argument in favour of the 

 latter. 



We now proceed to show that we can obtain an equation of the same 

 form asNos. 1 and 12, but differing from Nos. 13 and 1 4 in the value of 

 the constant K, if we drop altogether the assumption that equilibrium is 

 permanently maintained on the boundary between the particles and 

 the solution, i.e., that the concentration of the hydrogen-peroxide is 

 permanently maintained at zero. Instead we assume that the amount 

 Fdt acted upon in the time dt by each particle is proportional to the 

 concentration C' of the solute actually in contact with it. Retaining 

 the same notation we employed above, we thus have 



........................ (18), 



a being a constant. The amount of substance removed on the surface 

 of the particle must be replaced by diffusion from the interior of the 

 solution as a discontinuity of concentration would otherwise occur. It 

 can be expressed in terms of K, y and D - C' by making use of Equation 9. 

 This Equation was deduced on the assumption that the concentration 

 on the surface of the particles is zero. As absolute values of concen- 

 tration do not occur in Fick's law of diffusion, it is evident that we may 

 generalise the result so as to comprise the case that the concentration 

 on the surface of the particles is C' by replacing D of Equation 9 by 

 the difference D - C'. We thus obtain 



Fdt = 47TKry (D - C') dt ..................... (19) 



Eliminating C' from Equations 18 and 19, we find 



a, 



CLT + 



from which we deduce a formula identical with No. 12, by reason- 

 ing exactly analogous to that employed to establish it. The constant 

 K in the present case, however, has the value 



the number y varying according to the amount of convection from 1 to 

 infinity, as is clear from Equation 10, and the number a having any 

 positive value, which may be called the velocity constant proper of the 

 reaction. 



Thermodynamical Criticism of Nernst's Hypothesis. In conclusion, it 

 may be useful to criticise the principle put forward by Nernst from a 

 thermodynamical point of view. The essence of it is contained in the 

 following two sentences : " Many facts lead to the assumption that 

 equilibrium is established on the boundary of two phases, with 



